This invention pertains to a method and apparatus for debarking logs, and more particularly, to such a method and apparatus which are specially designed to handle logs having long-fibre bark.
For years, logs which have long-fibre bark have created serious problems for rotary ring-type debarkers. Bark leaving such a log tends to come off in long ropes which tend to ball up and create a tangled jam in and around the ring or rotor.
Others in the past have attempted to address this problem, but not with the high degree of success which the industry would like. For example, Palmquist, in U.S. Pat. No. 3,991,800, discloses a log-debarking machine which is intended to avoid the long-fibre bark problem. Featured in this machine are two hollow, rotor-type processing units, with the upstream unit having tools designed to produce a helical cut in bark, and with the downstream unit including revolving tools that further loosen and remove the bark from a log's surface. The upstream unit does not remove any bark. With all bark removal occurring solely in the downstream unit, there is still a clear opportunity for removed bark to create a jam.
Continuing to recognize the need for significant improvement in dealing with this problem, the industry later developed the rotary cutterhead-type debarker. In this kind of machine, plural (typically three) rotary cutterheads, which look somewhat like helical gears, are carried on arms, and rotate at high speed to cut and scrub against the outside surface of a log. Illustrative of such a debarker is the Ishida Brunette IBD-N360.500 debarker. While this kind of a machine has proven to be extremely effective in removing long-fibre bark with avoidance of the tangle/jam situation, it offers relatively low throughput speed.
With this background in mind, a general object of the present invention is to address the long-standing challenge of removing long-fibre bark from a log successfully, at the highest-possible throughput speed.
According to a preferred embodiment of the invention, the same proposes a unique linkage between a cutterhead-type debarker and a scraper-type debarker. Proposed, therefore, according to the invention, is an upstream debarking station in which rotary cutterheads are employed partially to remove bark, in such a manner that an emerging log has a bark/no-bark, "barber-pole" pattern on its surface. Travel through this first debarking station, where only partial debarking takes place, is characterized by relatively high throughput speed. Cooperating with this first, upstream debarking station is a second, downstream station in which remaining bark is removed by scraper arms carried on a rotary ring.
The method of the invention can be described as performing a first, partial debarking operation to produce a bark/no-bark, barber-pole pattern on a log, which pattern is characterized by alternating zones of bark and no-bark, and thereafter performing a second debarking operation to remove the remaining bark.
Experience has shown that by using cutterheads to create partial bark removal as described, remaining bark can easily be handled by well-known scraper arms. No balling-up or tangling occurs. And, with the cutterheads not being relied upon to do all of the debarking, it is possible to achieve successful debarking with satisfactorily high throughput rates.
Still another important feature of the system proposed by the present invention is that it is readily "convertible" to handle high-speed debarking of non-long-fibre-bark logs in areas where both kinds of logs are available for processing. The conversion alluded to is accomplished simply by shifting the cutterheads in the upstream debarking station away from the path of a log so that the log only engages the blades in the scraper-type debarker.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.